1. Field of the Invention
The present application relates generally to the field of ventilating, heating, and cooling systems for the creation and distribution of comfort air and the thermal management of sensitive systems for which temperature control is important.
2. Description of the Related Art
Heating and cooling to achieve comfort and to manage the temperature of critical systems and equipment is primarily accomplished through centralized systems. In these systems, hot and cold working fluids are used to provide temperature control for target objects within comparatively large volumes and surrounding structures. The system's capacity must be sized to heat or cool the target objects plus the thermal loads of the surrounding structures, extraneous objects and barrier materials. Heating and cooling of objects other than the targets results in significant energy waste, and slower response time for the system.
Variations of this system configuration involve conveying the working fluids conditioned in the central system to separate areas by means of specific ducts. This approach also suffers from the energy losses described above.
In buildings, centralized heating and cooling systems are used to establish and maintain occupant comfort, and in special cases, the temperature control of sensitive electronic equipment. These systems create and distribute heated and cooled air from a central point. The system is subject to significant losses as only a fraction of the thermal power developed by the central system reaches the target objects as the majority of the thermal capacity is wasted conditioning walls, ducting, ceilings, windows and furniture. Centralized heating and cooling systems with rotating mechanical parts tend to be noisy, and are subject to seal and other mechanical failures. The systems use ozone depleting refrigerants such as R-134A. With the exception of heat pump systems which operate over a narrow temperature range, a separate unit is required for heating.
Building heating and cooling is also provided by smaller, localized units, however such units utilize compressors for cooling which are noisy, vibrate, and utilize mechanical parts subject to failure, use ozone depleting refrigerants, and an additional unit is required for heating. The use of thermoelectric devices for these applications has been limited as they suffer from poor efficiency and use too much thermoelectric material to provide the needed capacity within cost constraints.
In automobiles, air is forced across an evaporator core within a centralized air handler unit to provide cool air to the passenger cabin in hot conditions. The cold air created in the air handler unit is distributed through a series of valves and air ducts to cool passengers. Such a system may supply 3,000 to 4,500 watts of cooled air at a steady state condition, of which the passengers require (and receive) only a small fraction. The majority of the cooled air is spent lowering the temperature of other parts of the cabin including the windows, head liner, seats and flooring. In addition, the cooling devices of such systems use chemicals such as R-134A with a high Green House Gas Index and operate with moving mechanical parts subject to failure.
In heating mode, the air handler unit provides heating through the same distribution system and suffers losses similar to those experienced by A/C systems as the majority of the warmed air is spent heating various elements of the cabin other than the occupants. Also, since waste heat from the engine coolant is used to heat occupants, the response time is slow. This is especially true for small-engine efficient vehicles such as diesels and hybrids. This condition has been recognized and Positive Temperature Coefficient (PTC) heaters are used to supplement engine coolant heating. However, such devices are inefficient.
The Climate Controlled Seat System (CCS™) described by Feher (U.S. Pat. No. 4,923,248, issued May 8, 1990, “Cooling and Heating Seat Pad Construction”), provides a thermoelectric system for distributed heating and cooling by embedding heating and cooling devices within an occupant's seat back and cushion, however it only partially addresses the need for occupant comfort because the human body requires heating and cooling of surfaces not touching the seat and backrest. In addition, the thermal capacity of the device is limited by the use of air as the sole working fluid due to its low heat capacity.